Commutated wound armature assemblies

ABSTRACT

Winding configurations for the armature of small commutator type motors are disclosed in which a first winding can be identified as just completing commutation at one brush at the same time that a second winding is in the midst of being short circuited by the other brush. The windings are distributed and arranged to be closely coupled to each other by having coil sides of each winding in slots common to both. In this manner, the abrupt current change required by the commutation process can be compensated for by an opposite change in current in the coupled short-circuited winding and with a minimum instantaneous flux change. This results in significantly reduced sparking, longer brush and commutator life and reduced electromagnetic interference (EMI).

111 3,733,506 1 May 15, 1973 COMMUTATED WOUND ARMATURE ASSEMBLIESInventors: Wolfgang Jaffe, Roselle Park; John W. Wurst, Dover, both ofNJ.

Assignee: The Singer Company, New York,

Filed: Oct. 29, 1971 Appl. No.: 193,934

US. Cl. ..310/198, 310/220, 310/223 Int. Cl...., ..H02k 3/16 Field ofSearch ..310/189, 198-207,

References Cited UNITED STATES PATENTS FOREIGN PATENTS OR APPLICATIONS297,958 4/1954 Switzerland ..310/225 Primary Examiner-D. F. Duggan Ahomey-Marshall J. Breen et al.

[ 57] ABSTRACT Winding configurations for the armature of smallcommutator type motors are disclosed in which a first winding can beidentified as just completing commutation at one brush at the same timethat a second winding is in the midst of being short circuited by theother brush. The windings are distributed and arranged to be closelycoupled to each other by having coil sides of each winding in slotscommon to both. In this manner, the abrupt current change required bythe commutation process can be compensated for by an opposite change incurrent in the coupled short-circuited winding and with a minimuminstantaneous flux change. This results in significantly reducedsparking, longer brush and commutator life and reduced electromagneticinterference (EMI).

4 Claims, 8 Drawing Figures PATENIEUHAY 1 51073 SHEET 1 OF 3 (PRIOR ART)Fig. I

PATENTEDHAYWWB 3,733,506

SHEET 2 [IF 3 PATENTED HAY I 5 I975 SHEET 3 OF 3 i I hid I wM w l5COMMUTATED WOUND ARMATURE ASSEMBLIES FIELD OF THE INVENTION Thisinvention is related to winding arrangements for the armature coils ofsmall commutator motors preferably of the type having two diametricallyspaced brushes and suitable for driving sewing machines, portable toolsand the like. These winding arrangements result in significantlyimproved commutation with respect to that obtained by prior art armaturewindings.

DESCRIPTION OF THE PRIOR ART Substantially all of the prior art motorsof the type to which the present invention relates have employed simplelap-wound armatures of the single coil type. While the commutation ofthese prior motors has been notably poor, little effort has been made toimprove the commutation at its source by special armature windingconfigurations. Rather, the practical approach has been through the useof special brush material to increase useful brush life to a tolerablelevel but leaving the commutation relatively unaffected. Whereelectromagnetic interference has been a problem, resort has generallybeen made to the use of conventional line filters and shielding whichmerely isolated the interference without doing anything about its basicsource, viz., poor commutation; It has been suggested by the prior artthat a physically more-compact armature winding results if a distributedcommutated winding is used to reduce the end-turn build up. This isshown in the Hunsdorf US. Pat. No. 2,779,886. However, in this priorinvention the improvement resides only in lower armature co'pper lossesand no claim is or can be made for improved commutation which is theessential attribute of the present invention.

SUMMARY OF THE INVENTION In accordance with the teachings of the presentinvention, the armature windings between adjacent commutator bars arenot lumped but are distributed over several slots so that the windingjust completing commutation at one brush may be closely coupled toanother winding which is, at that moment, in the midst of beingshort-circuited through the other brush. This is accomplished byarranging the individual armature coils so that the commutated windingshares as many slots as possible in common with the short-circuitedwinding. In this manner the abrupt change in the current in the coilsundergoing commutation is compensated by an opposite change in currentproduced in the coils which are short-circuited and with minimuminstantaneous flux change thus resulting in minimum sparking betweenbrushes and commutator. If this coupling were perfect there would be nosparking voltage and perfect commutation would result. In practice andaccording to this invention it is possible to obtain sufficiently closecoupling to significantly improve the commutation and without requiringwinding configurations which are too complicated to wind practically.

DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 is a schematic diagram of a conventional prior art single-coillap winding applied to a two-pole armature having 1 1 bars and l 1 slotswith a coil pitch of 1-5.

FIG. 2 is a schematic diagram showing the winding configuration betweenadjacent commutator bars for an ll bar, 11 slot armature embodying thisinvention.

FIG. 3 is a schematic diagram showing the coupled relation betweenwindings made in accordance with the embodiment of FIG. 2.

FIG. 4 is a schematic diagram showing a further embodiment of thepresent invention and derived as a simplification of the embodiment ofFIG. 3.

FIG. 5 is a schematic diagram of a conventional prior art single-coillap-winding applied to a two-pole armature having 22 bars and 11 slotswith a coil pitch of 1-5.

FIG. 6 is a schematic diagram of an armature winding for a two-pole, 22bar, l l slot armature illustrating an embodiment of this invention.

FIG. 7 is a schematic diagram of a conventional prior art single-coillap-winding applied to a two-pole, 12 bar, 12 slot armature having acoil pitch of l6.

FIG. 8 is a schematic diagram of an armature winding for a two-pole 12bar, 12 slot armature illustrating a further embodiment of thisinvention.

A word of explanation which applies to all the figures is in order. Ineach figure the top series of rectangles represent the armature teeth sothat the spaces between rectangles represent the armature slots. This isa flat development of the armature and the first tooth at the left isrepeated as the last tooth at the right. The series of connectedrectangles below the armature teeth in each figure represent thecommutator ring of bars with each vertical line representing theinsulation between bars.

Each figure, except FIG. 2, represents a specific moment in time atwhich one winding is just completing its commutation at one brush. Itwill be understood that a moment later commutation will be completed atthe other brush with respect to the winding which was short-circuitedbefore and this process continues as the armature rotates with respectto the brushes. One brush is just completing the commutation of onewinding at which time the other brush is short-circuiting a secondwinding and this occurs successively on an alternating basis withrespect to the two brushes. The current in each winding must be reversedin the time required for the insulated segment to pass under one brush.Only two (or three) windings are shown in the drawings for simplicitybecause these windings are the only ones affecting the commutation atthe moment and to show other windings would only needlessly complicatethe picture. It will be understood that a complete armature hasadditional windings identical to those shown so that all slots aresymmetrically filled with coil sides and form two parallel paths forcurrent flow between the brushes in accordance with ordinary armaturewinding techniques. The point is that the winding relationship shown anddefining this invention exists successively for every winding as itcompletes its commutation and so is effective for the commutation as awhole. Thus by establishing the coupling relationship between twospecific windings at the moment of completing the commutations of onewinding this invention is defined with respect to a fully woundarmature.

Referring now to FIG. 1 which shows a lap winding of conventional priorart type having single coils between adjacent commutator bars, it willbe seen that winding 10 having a coil side 11 lying in slot 12 and coilside 13 lying in slot 14 is in the midst of being shortcircuited throughbrush 15 which spans commutator segments 16 and 17. At the same timewinding'l8 having coil sides 19 and 20 lying in slots 21 and 22respectively, is just completing its commutation because brush 23 isjust moving out of contact with segment 24. The coil sides of thewinding just completing commutation will be conveniently distinguishedin all the drawings by the double arrows applied to the coil sides. Itwill be observed that no coil side of winding 10 lies in the same slotwith a coil side of winding 18 as required by the teachings of thisinvention. Thus there is very little mutual'couping between thesewindings and the abrupt change of current in winding 18 required by thecommutation process cannot be balanced by a mutual change of current inwinding 10. This results in the generation of a sparking voltage inwinding 18 which produces destructive arcing as brush 23 leaves contactwith segment 24. This also produces electrical noise interference whichmay have adverse effects on nearby radio and television receivers as iswell known.

FIG. 2 is illustrative of a winding configuration for an 11 bar, 11 slotarmature made in accordance with the present invention and presents asingle typical winding between adjacent commutator bars which has, forthis embodiment, six coil sides in six different slots. It will be notedthat this arrangement of distributed coils provides a maximum number ofslots for common coupling with another similar winding, which istheunderlying principle of this invention. In comparison with theconventional lap winding of FIG. 1, the single-coil winding 10 has nowbeen distributed in three coils 10a, 10b and 10c, each having a pitch ofl-5. Coil 10a is wound in a forward direction and coils 10b and 10c arewound in a backward direction. It will be seen that the winding of FIG.2 covers essentially the entire periphery of the armature with therelatively reversed coils being necessary to make the torque produced byeach coil side additive.

FIG. 3 is a schematic diagram showing the coupling between two windings,each of the same configuration as the single winding shown in FIG. 2.windings 10 and 18 are now each distributed in six slots instead of twoas in FIG. 1. It will be noted that there are five slots 8,, S S S S,which contain coil sides common to both windings. This providessubstantial mutual coupling between the windings 10 and 18 and permitscurrent change in winding 18 with less flux change than with thearrangement of FIG. 1. Thus the sparking voltage generated in winding 18of FIG. 3 is reduced and the commutation is accordingly improved.Further, the winding 18 of FIG. 3, being distributed, has lessselfinductance than the winding 18 of FIG. I which is lumped in one coilper bar. Since self-inductance is a measure of the kinetic energystorage capability, the winding 18 of FIG. 3 cannot store and thereforecannot later release as much energy as winding 18 of FIG. l. Thus theenergy available for generating sparking voltage is less and thecommutation is accordingly improved.

FIG. 4 shows the application of the principle of this invention to thesame armature core as shown in FIG. 1 and omitting the reverse coils inFIG. 2 and 3. Windings l and 18 are now each distributed in four slotsinstead of two as in FIG. 1. It will be noted that coil side 30 ofwinding now occupies the same slot as coil side 31 of winding 18 whichprovides mutual coupling between the windings and permits current tochange in winding 18 with less flux change than with the arrangement ofFIG. 1. Thus the sparking voltage generated in winding 18 of FIG. 4, isreduced and the commutation is improved. It will be seen that thewinding arrangement of FIG. 4 is a simplification derived from thearrangement of FIGS. 2 and 3 by omitting the single coils 10a and 18a.The windings in this case span approximately one-half the armatureperiphery and have the same winding direction. While the winding of FIG.4 is easier to apply, it yields a smaller mutal coupling and istherefore less effective in improving commutation than the arrangementof FIG. 3.

It will be understood that the embodiments thus far shown use 11 slotsonly asan example of the principle involved and it is not intended thatthis invention be limited to any specific number of slots, odd or even.A larger number of slots of course provides more slots for closercoupling possibilities, but the winding becomes more complicated.

Further, it is possible to apply the principle of this invention to anarmature having an even number of commutator bars. An example of thistechnique will be illustrated in FIG. 6 as applied to an armature having11 slots and 22 bars with a winding pitch of l-S. First, however, aconventional prior art lap winding for this armature is illustrated inFIG. 5. Referring to FIG. 5, the short-circuited winding 10 has nocoupling slots in common with the winding 18 which is just completingcommutation. A third winding 40 is also short-circuited but is notcoupled to the winding 18 by any common slot relation and the couplingconcept of this invention is not present.

Referring now to FIG. 6, a winding arrangement embodying this inventionis shown applied to the same core as shown in FIG. 5. This arrangementprovides a very high degree of coupling between the winding 18 justcompleting commutation and another winding 10 under short-circuitcondition. In this case each winding is distributed over substantiallythe entire armature periphery in six coil sides and of these, five coilsides lie in slots common to both windings.

If a brush wider than a commutator bar, as shown in FIG. 6 is used, anadditional short-circuited winding 40 is coupled through four commonslots with the winding 18 just completing commutation. It will beunderstood that the wide brush is not a limiting factor in thisinvention but its use does result in greater coupling between thewinding just completing commutation and windings which, at that moment,are short-circuited thus improving the commutation over that obtainablewith a narrower brush.

It will be seen in FIG. 6 that winding 10 consists of one coil 41forwardly wound in slots 42,43 and two coils 44, 45 each backwardlywound in slots 46, 47 and 48, 49 respectively. This winding 10 isshort-circuited through brush l5.

Winding 18 consists of one coil 51 forwardly wound in slots 49, 48 onecoil 52 backwardly wound in slots 43, 42 and one coil 53 backwardlywound in slots 54, 46. This winding 18 is just completing commutationthrough brush 23.

The winding 40, which is effective as a short-circuit coupled windingwhen a wide brush is used, is indicated in FIG. 6 by the superposed dotsand it will be seen that this winding shares slots 42, 43, 46 and 49 incommon with winding 18 and thus still further improves the coupling inaccordance with the teaching of this invention. It will be seen that thewindings of FIG. 6 which are connected between adjacent bars may becharacterized as being distributed over substantially the entirearmature periphery with the extreme coil sides spanning approximately360 electrical degrees. That is to say, if each winding is considered asa distributed winding with series-connected forwardly and backwardlywound coils, the extreme outside coil sides of the winding as a wholespan the entire number of slots in the armature. It will be furtherunderstood that, for a given multicoil winding, the number of turns ineach coil need not be but preferably is the same.

The principle of this invention may also be applied to armatures inwhich both slots andbars are an even number. This technique is shown inFIG. 8 as applied to an armature having 12 bars and 12 slots with a coilpitch of 16. First, however, a conventional single-coil lap-windingapplied to this same armature core is shown in FIG. 7 and it will beseen that coil which is short-circuited by brush has no coil sides inslots common to the coil sides of winding 18 which is just completingits commutation at brush 23. There is no mutual coupling in FIG. 7between windings l0 and 18 as defined by this invention and thecommutation will be accordingly poor.

Referring now to FIG. 8 and in full accordance with the principle of thepresent invention, winding 10 is now distributed in two series-connectedcoils, 10a and 10b. Coil 10a is forwardly wound and coil 10b isbackwardly wound. Similarly, winding 18 is now distributed in twoseries-connected coils, 18a and 18b. Coil 18a is forwardly wound andcoil 18b is backwardly wound. It will be noted that every coil side ofwinding 10 lies in a slot common to a coil side of winding 18. Theseslots are indicated as S S S and S and this configuration represents themaximum possible degree of mutual coupling between windings 10 and 18,all in accordance with the basic principle of this invention. In FIG. 8it will again be noted that the extreme coil sides of windings 10 and 18span substantially the full armature periphery.

From the above it will be evident that the present invention defineswinding arrangements for the armatures of small commutator type motors,which arrangements greatly improve the commutation of these motors.These arrangements are based on the principle of increased mutualcoupling between a winding which is being short-circuited by one brushand a second winding which, at the same time, is just completingcommutation by the other brush. This increased coupling is obtained bydistributing the windings between adjacent commutator bars over severalarmature slots and then arranging the coil sides of each winding to liein slots common to both windings. This may be done by a progressivewinding as in FIG. 3. which is distributed over approximately one-halfthe armature periphery or by a winding as in FIG. 5 which consists offorwardly and backwardly wound coils distributed over the entirearmature periphery.

Other modes of applying the principle of the invention may be employed,change being made as regards the details described provided the featuresstated in any of the following claims, or the equivalents of such, beemployed.

Having thus described the nature of the invention, what I claim hereinis:

1. A rotor assembly for an electric motor having brushes comprising: anarmature mounted for rotation about its axis, said armature having aplurality of slots equally spaced about its periphery, a commutator ringmounted to turn with said armature with its axis coinciding with saidarmature axis and divided into a plurality of bars of equal arcuatelength and insulated from each other for successive engagement with thebrushes of the motor, a plurality of coils wound in said slots, saidcoils being connected to define a first distributed winding between afirst pair of adjacent commutator bars and a second distributed windingbetween a second pair of adjacent commutator bars, certain of the coilsides of said first winding lying in the same slots as the coil sides ofsaid second winding to form mutual coupling between said windingswhereby when one winding is under commutation and/or just completingcommutation at one brush, the other winding is shortcircuited throughthe other brush.

2. A rotor assembly according to claim 1 in which each winding consistsof forwardly and backwardly wound coils and the extreme coil sides ofeach winding span approximately the full armature periphery.

3. A rotor assembly according to claim 2 in which one or more coil sidesof each winding lie in slots common to both windings.

4. A rotor assembly according to claim 1 in which each winding isprogressively distributed in the same direction and the extreme coilsides of each winding span approximately one-half the armatureperiphery.

1. A rotor assembly for an electric motor having brushes comprising: anarmature mounted for rotation about its axis, said armature having aplurality of slots equally spaced about its periphery, a commutator ringmounted to turn with said armature with its axis coinciding with saidarmature axis and divided into a plurality of bars of equal arcuatelength and insulated from each other for successive engagement with thebrushes of the motor, a plurality of coils wound in said slots, saidcoils being connected to define a first distributed winding between afirst pair of adjacent commutator bars and a second distributed windingbetween a second pair of adjacent commutator bars, certain of the coilsides of said first winding lying in the same slots as the coil sides ofsaid second winding to form mutual coupling between said windingswhereby when one winding is under commutation and/or just completingcommutation at one brush, the other winding is short-circuited throughthe other brush.
 2. A rotor assembly according to claim 1 in which eachwinding consists of forwardly and backwardly wound coils and the extremecoil sides of each winding span approximately the full armatureperiphery.
 3. A rotor assembly according to claim 2 in which one or morecoil sides of each winding lie in slots common to both windings.
 4. Arotor assembly according to claim 1 in which each winding isprogressively distributed in the same direction and the Extreme coilsides of each winding span approximately one-half the armatureperiphery.